‘I would like to have a cat,’ he said after a while. ‘I do miss cats.’

‘Tell me about the summoning.’

‘You know it all already!’ he said indignantly. ‘Nimue will find Excalibur, she will fetch poor Gwydre, and the rites will be done properly. Here, on the mountain. But will the Gods come? That is the question, isn’t it? You worship Mithras, don’t you?’

‘I do, Lord.’

‘And what do you know of Mithras?’

‘The God of soldiers,’ I said, ‘born in a cave. He is the God of the sun.’

Merlin laughed. ‘You know so little! He is the God of oaths. Did you know that? Or do you know the grades of Mithraism? How many grades do you have?’ I hesitated, unwilling to reveal the secrets of the mysteries. ‘Don’t be absurd, Derfel!’ Merlin said, his voice as sane as it had ever been in all his life. ‘How many? Two? Three?’

‘Two, Lord.’

‘So you’ve forgotten the other five! What are your two?’

‘Soldier and Father.’

‘Miles and Pater, they should be called. And once there were also Leo, Corax, Perses, Nymphus and Heliodromus. How little you know of your miserable God, but then, your worship is a mere shadow worship. Do you climb the seven-runged ladder?’

‘No, Lord.’

‘Do you drink the wine and bread?’

‘That is the Christian way, Lord,’ I protested.

‘The Christian way! What halfwits you all are! Mithras’s mother was a virgin, shepherds and wise men came to see her newborn child, and Mithras himself grew to become a healer and a teacher. He had twelve disciples, and on the eve of his death he gave them a final supper of bread and wine. He was buried in a rock tomb and rose again, and he did all this long before the Christians nailed their God to a tree. You let the Christians steal your God’s clothes, Derfel!’

I gazed at him. ‘Is this true?’ I asked him.

‘It is true, Derfel,’ Merlin said, and raised his ravaged face to the crude bars. ‘You worship a shadow God. He is going, you see, just as our Gods are going. They all go, Derfel, they go into the void. Look!’ He pointed up into the clouded sky. ‘The Gods come and the Gods go, Derfel, and I no longer know if they hear us or see us. They pass by on the great wheel of heaven and now it is the Christian God who rules, and He will rule for a while, but the wheel will also take Him into the void and mankind will once again shiver in the dark and look for new Gods. And they will find them, for the Gods come and they go, Derfel, they go and they come.’

‘But Nimue will turn the wheel back?’ I asked.